1. Field of the Invention
The invention relates to a monopole antenna, and particularly to a planar inverted F antenna fabricated in an integrated manner and adopted for use on a wireless communication device to provide high antenna performance for the wireless communication device.
2. Description of the Related Art
With the wireless communication industry is expanding in recent years, wireless communication technologies have become widely used in a great number of high-tech products. Nowadays proliferations of wireless communication products are available on the market. The prevailing trend in wireless communication products is slim and light without compromising performance to meet consumers' requirements of high quality. Hence the antenna that transmits and receives signals for wireless communication products is an important item in research and development.
The commonly used antennas include dipole antennas, helix antennas, planar inverted F antennas (PIFA), microstrip antennas and the like. The PIFA can achieve impedance matching without adding inductance and capacitance, thus it is widely used.
Refer to FIG. 1 for a PIFA 100, as disclosed in U.S. Pat. No. 6,795,028 B2, includes a first conductive blade 110, a second conductive blade 120, a short blade 130, a feed blade 140 and a feed connector 150. The first conductive blade 110 is the main radiation portion. The second conductive blade 120 is grounded and has a length slightly greater than that of the first conductive blade 110 but with a width no larger than that of the first conductive blade 110. The short blade 130 bridges one end of the first and second conductive blades 110 and 120, and has a width slightly smaller than that of the first and second conductive blades 110 and 120. The feed blade 140 is located between the first and second conductive blades 110 and 120, and has a width the same as the first and second conductive blades 110 and 120 but with a length slightly smaller than that of the first conductive blade 110. The feed blade 140 has one edge connecting to an edge of the first conductive blade 110 to form a line. Hence another edge of the feed blade 140 is spaced from the short blade 130 at a small distance. The feed connector 150 has a center conductor 152 running through the second conductive blade 120 to brace the feed blade 140. The feed blade 140 and the first and second conductive blades 110 and 120 are parallel with one another. The short blade 130 and the feed connector 150 are normal to the feed blade 140 and first and second conductive blades 110 and 120. Thus when the antenna is in operation, the feed blade 140 and the second conductive blade 120 create a capacitance effect to feed capacitance to the first conductive blade 110.
FIG. 2 illustrates another PIFA disclosed in U.S. Pat. No. 6,781,547 B2. The antenna 200 is formed on an upper surface of a substrate 250 and includes a round opening 252, a slot 254, two radiation conductive wires 210 and 212, and a straight radiation conductive wire 214. The straight radiation conductive wire 214 has a feed point 240 on one end not connecting to the radiation conductive wire 212. The two radiation conductive wires 210 and 212 have a plurality of apertures 256 evenly formed thereon and they run through the substrate. The apertures 256 may also be formed on the straight radiation conductive wire 214 if necessary. The round opening 252, slot 254 and apertures 256 can increase the bandwidth and gain of the antenna 200. In addition, the substrate 250 may be a printed circuit board. The substrate 250 has a lower surface made from a conductive material to become a ground surface 220. The ground surface 220 may be located beneath the radiation conductive wire 210 and a portion of the straight radiation conductive wire 214 (e.g., one half of the straight radiation conductive wire 214).
While the conventional antenna can be shrunk without reducing its performance, the fabrication cost is still high and fabrication is difficult. To produce a low cost antenna with high performance and a simple fabrication process is still an issue continuously pursued in the industry.